The problems experienced by Northern Rock's website last week highlight how critical it is for businesses to ensure their websites continue to perform during unexpected peaks in demand.
Northern Rock's website slowed down dramatically when hundreds of thousands of anxious customers accessed it at the same time, leaving many unable to view their accounts.
The failure added to the sense of public panic after Northern Rock sought emergency funding from the Bank of England, leaving customers desperate to get news about their accounts.
Financial websites like Northern Rock's are critical not only for banking customers that manage their accounts online, but also as a source of information and updates.
Following the website problems, Northern Rock said in a message to customers: "Thank you so much for your patience, particularly when using our website which has been running very slowly due to the number of people working online."
Clive Longbottom, service director at analyst firm Quocirca, said, "It appears the bandwidth available to the Northern Rock website was not enough, and the hardware supporting the website could not handle the number of visitor requests.
"There are certain things that can be done to prepare for this, such as web accelerators and timing systems that automatically take people to another site specifically to tell them that they have not been forgotten."
Nick Staib, an internet banking spokesman at HSBC, said the bank has invested in technology to ensure its website performs with dual site contingency and strong multiple server resilience.
"Capacity is based on anticipated peak volumes several years ahead. We are continually monitoring our data operations. Any deviations are quickly escalated and investigated.
"We run many diagnostic tests, including dummy transactions, through special test accounts to check real world performance against service level agreements. We have added, and will continue to add, extra capacity as and when required."
A spokesman at HBOS said, "We are continually reviewing the architecture of the site to ensure that it meets our projected customer activity levels while allowing for periods of "stretch" where demand is higher than normal.
"As a large business, we also have contingency plans to cover other eventualities and ensure customers' inconvenience would be kept to a minimum should exceptional circumstances arise."